There's some serious money to be had in this market. I would actually argue this a very low amount.
http://www.marketresearchmedia.com/?p=568
http://wikibon.org/wiki/v/Big_Data_Database_Revenue_and_Mark...
http://www.marketresearchmedia.com/?p=568
http://wikibon.org/wiki/v/Big_Data_Database_Revenue_and_Mark...
From the little I have seen of NoSQL, I like it as a niche use-case DB, not entirely divorced from a RDMBS. Thus, not surprised it has the potential to grow like crazy.